JPH08316938A - Optical communication method and optical communication system for multiplexing plural channels - Google Patents

Abstract

PURPOSE: To provide the optical communication system which easily allows the variance of light sources in the system. CONSTITUTION: Each of plural channels consists of a wavelength group of plural wavelengths which have prescribed wavelength intervals. One of plural wavelengths constituting one channel is used for transmission on the transmission side, and light is detected on the reception side by an optical detection means which has (natural number)-fold detection rate peaks of the prescribed wavelength interval. When the wavelength received at a first point of time and another wavelength of a wavelength interval exceeding the detection rate peak interval in the optical detection means of an optical node for reception are received at a second point of time, the detection rate peak different from that for detection of the wavelength received at the first point of time is used to perform the reception. The extent or movement or the detection rate peak for movement from the first point of time to the second point of time doesn't exceed the detection rate peak interval.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wavelength division multiplexing for multiplexing a plurality of wavelengths in an optical transmission line.

[0002]

2. Description of the Related Art In a wavelength division multiplexing optical communication system, optical signals of different wavelengths are transmitted on one transmission line to improve the utilization efficiency of the transmission line. Usually, such a system has a plurality of stations that transmit optical signals of different wavelengths, an optical merging unit that puts these optical signals into a transmission line, the transmission line, and only the required wavelength from the wavelength-multiplexed signal. It is composed of wavelength separating means for separating and a plurality of stations for receiving this signal.

In such a system, a semiconductor laser (hereinafter referred to as LD) as a light source provided in each terminal station, an optical fiber as a transmission line, an optical merging element composed of a half mirror or an optical waveguide as an optical merging means, and an optical wavelength as a wavelength separating means. A filter (hereinafter referred to as an optical filter) is mainly used.

As the transmission / reception method, the transmission wavelength on the transmission side is fixed and the reception wavelength on the reception side is made variable to select a desired wavelength on the reception side, or the reception wavelength on the reception side is fixed and the transmission side is fixed. There is a method in which the transmission wavelength is variable and the wavelength is selected so that the transmission side can receive the signal at a desired destination, and a method in which the wavelength is variable on both the transmission side and the reception side.

As an example of an LD whose wavelength can be changed, a publication, IEICE OQE89-116, “Three-electrode long resonator λ”
/ 4 shift MQW-DFB laser ”described in DFB (Dist
ributed Feed Back) -LD can be mentioned. Further, an FFP (Fibre Fabry-Perot) filter or the like is known as an optical filter for extracting a desired wavelength from a wavelength-multiplexed optical signal. Publication Electronics Let as an example
ters, 1990, Vol. 26, No. 25, pages 2122-2123, "PASSIVELY TEMPE
RATURE-COMPENSATED FIBRE FABRY-PEROT FILTER AND IT
S APPLICATION IN WAVELENGTH DIVISION MULTIPLE ACCE
FFP (Fiber Fabry Per) described in SS COMPUTER NETWORK
ot) A filter can be mentioned.

[0006]

However, an FFP filter or the like has a plurality of transmittance peaks, and its optical frequency interval is generally called FSR (Free Spectral Range). Such a filter corresponds to FSR. A plurality of wavelengths having a wavelength interval ΔλFSR or a wavelength interval of an integral multiple thereof cannot be distinguished. Therefore, the wavelength region in which wavelength multiplexing is performed is limited to the range of ΔλFSR corresponding to one FSR of the optical filter. The conceptual diagram of the wavelength multiplexing is shown in FIG. The horizontal axis is the wavelength λ, the vertical axis is the light intensity,
λf1 and λf2 are wavelengths indicating the ends of the wavelength interval corresponding to one FSR (optical frequencies f1 to f2). λ1 to λm are terminal stations 1
The transmission wavelengths of .about.m and .lamda.min to .lamda.max represent the wavelength regions used by the system.

Further, since it is necessary that the emission wavelengths of all the light sources in the communication system be included within the range of ΔλFSR, it is not possible to use light sources having significantly different emission wavelengths, and many light sources having emission wavelengths close to each other can be used. I had to prepare.

A first object of the present application is to extend the wavelength range used in the system beyond the ΔλFSR of the optical filter.

A second object of the present application is to allow variations in the emission wavelength of the light source to eliminate the need for wavelength selection.
It is to increase the yield.

[0010]

In order to achieve the above-mentioned object, the present invention has the following objects: 1) A plurality of optical nodes are connected by an optical transmission line, and a plurality of channels are multiplexed in the optical transmission line for communication. In the optical communication method in an optical communication system for performing, each of the plurality of channels is configured by a wavelength group including a plurality of wavelengths having a predetermined first wavelength interval, and one optical node for transmitting is provided. An optical node that transmits and receives at one wavelength of a wavelength group that configures a channel is an optical detection unit that detects light in the optical transmission line, and has a plurality of detection rate peaks that are equal to the predetermined detection peaks. There is provided an optical communication method characterized in that a photodetection rate peak of a photodetector having a natural number multiple of a first wavelength interval is received in conformity with a wavelength constituting a wavelength group of a desired channel. When receiving a wavelength received at the first time point and another wavelength having a wavelength interval exceeding the detection rate peak interval of the light detection means of the optical node performing the reception at the second time point, It is possible to receive by using a detection rate peak different from the detection rate peak that has detected the wavelength received at the time point. The movement amount of the detection rate peak when moving from the first time point to the second time point does not exceed the interval of the detection rate peaks.

2) In the optical communication method of 1), the second wavelength interval that does not interfere with at least wavelengths that belong to different channels and that are closest to each other so that wavelengths that belong to different channels do not cause interference. By arranging with, interference between different channels can be prevented.

3) Further, in the optical communication method of 2), a plurality of wavelengths are arranged at the second wavelength interval so that the wavelengths are within the predetermined first wavelength interval, and the plurality of wavelengths are mutually arranged. Channels can be easily set by belonging to different channels.

4) Further, in the optical communication methods of 1) to 3), the optical node which has generated the transmission request by allocating the plurality of channels to each of the optical nodes performing the transmission does not undergo a channel allocation operation or the like. You can start sending immediately.

5) On the other hand, in the optical communication method of 1) above,
The optical node that performs the transmission is a photodetection unit that detects light in the optical transmission line, and is a photodetection unit that has a plurality of detection rate peaks at the predetermined first wavelength interval, and at least the predetermined detection wavelength peak. By scanning the first wavelength interval to detect a channel in use and transmitting at one wavelength in a wavelength group forming a channel that does not cause interference with the channel in use, each channel is previously set. Communication can be performed without being assigned to a node, and only the channel in use exists in the transmission path, so that the channel area can be used efficiently.

6) Further, in the optical communication method of 5), the optical node for transmitting detects a channel in use in the optical transmission path including a channel transmitted by the own node by the optical detecting means, This detects the interval between the channel transmitted by the local node and the channel detected closest to the channel transmitted by the local node among other channels in use, and controls the wavelength at which the local node transmits the interval. Then, by maintaining the predetermined interval, the channels are sequentially multiplexed at the predetermined interval, so that the channel region can be used more efficiently.

7) Further, the optical communication system of the present invention is an optical communication system in which a plurality of optical nodes are connected by an optical transmission line and a plurality of channels are multiplexed in the optical transmission line for communication. Each of the plurality of channels is composed of a wavelength group consisting of a plurality of wavelengths having a predetermined first wavelength interval, and an optical node for transmission is one of the wavelength groups forming one channel. An optical node for transmitting light at one wavelength is a light detecting means for detecting light in the optical transmission line, and an optical node for receiving light has a plurality of detection rate peaks that are equal to the predetermined first peak. Provided is an optical communication system comprising: a photodetector having a natural multiple of a wavelength interval; and a device for matching a photodetection rate peak of the photodetector with a wavelength forming a wavelength group of a desired channel. To do.

In the optical communication system of 8) and 7),
The light detecting means has a periodic transmittance peak, and the light detecting means having a plurality of detection peaks is simplified by including an optical filter capable of controlling the transmittance peak while maintaining the period. Can be configured to.

[0018]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

In the present application, the principle and operation will be described using wavelength instead of optical frequency. here,
The wavelength λ and the optical frequency ν can be mutually converted based on the relationship of λ = c / (nν). c is the speed of light, n is the refractive index of the medium, and both are constants.

Further, the FSR of the optical filter, which is originally an amount representing the "optical frequency interval", will be described as "wavelength interval" in the embodiments.

FIG. 3 is a block diagram of the optical communication system of this embodiment. This is a star-type network with n terminal stations, and the entire network is terminal stations 301-1 to -n, optical nodes 302-1 to -n, nxn star coupler 303, optical fibers 304-1 to -n, 305-1. ~ -N.

Each of the terminal stations 301-1 to -n has an optical node 302-1.
~ -N and optical fibers 305-1 to -n for reception are connected to the nxn star coupler 303. The transmission light from the optical transmitter is sent to the n × n star coupler 303 through the transmission optical fibers 304-1 to -n. The n × n star coupler 303 evenly distributes the transmitted light to the respective receiving optical fibers 305-1 to −n and each optical node 302−
Send to 1 to -n.

FIG. 4 is a block diagram of the optical node 302. The whole is composed of an optical transmitter 401 and an optical receiver 402.

FIG. 5 is a block diagram of the optical transmitter 401. The whole is composed of a control circuit 501, an LD drive circuit 502, an LD 503, a light receiving element 504, an amplifier 505, a temperature controller 506, and an optical branching device 507.

The control circuit 501 outputs a control signal to the LD drive circuit 502 based on the control signals from the terminal station and the amplifier 505. The LD drive circuit 502 outputs L based on the control signal.
Drive current is output to D503. In addition, the modulation current is output to the LD 503 based on the transmission signal from the terminal station. The LD 503 outputs the signal light to the optical branching device 507. The optical splitter 507 is an LD
The signal light from 503 is split into two, and one is output to the transmission line and the other is output to the light receiving element 504.

FIG. 6 is a block diagram of the optical receiver 402. The whole is composed of a wavelength control circuit 601, a filter drive circuit 602, an optical filter 603, a light receiving element 604, and an amplifier 605.

The optical signal from the transmission line enters the optical filter 603. The transmitted light enters the light receiving element 604, is converted into an electric signal, is amplified by the amplifier 605, and is input to the wavelength control circuit 601. The wavelength control circuit 601 consists of a control signal from the terminal and an amplifier 6
Based on the received signal from 05, a control signal is output to the filter drive circuit 602 to control the transmission wavelength of the optical filter.
Also, the received signal is output to the terminal station.

Here, it is assumed that the change amount ΔVF of the control voltage VF to the optical filter drive circuit 602 and the change amount ΔλF of the transmission spectrum of the optical filter 603 are proportional.

FIG. 7 is a diagram showing a transmission spectrum of the optical filter 603. The horizontal axis is the wavelength λ, and the vertical axis is the transmittance T, λ
f1 to λf5 are the central wavelengths (hereinafter referred to as filter transmission wavelengths) of the m to m + 4th-order transmittance peaks at a certain moment. As shown in the figure, there are a plurality of transmission spectra at fixed intervals, and the intervals are ΔλFSR. Further, ΔλBW represents the band width (Band Width) of the transmission spectrum, and λA to λB represent the wavelength range usable as the optical filter.

The control circuit 501 monitors the output of the amplifier 505 and keeps the output light intensity of the LD 502 constant. The temperature controller 506 keeps the temperature around the LD 502 at a predetermined value. Terminal
The transmission wavelength of i is set so as to have a unique wavelength λi. Although only temperature control is performed in this embodiment, if more accurate stabilization of the transmission wavelength is required, some wavelength reference and wavelength discriminating means are introduced, and a part of the output light is branched and used as a reference. And a method of feeding back the obtained error to the LD drive current.

The optical filter 603 has a plurality of transmittance peaks as shown in FIG. For adjacent peaks, the wavelength difference is ΔλFSR.

Next, the features of this embodiment will be described.

In this embodiment, a set of wavelengths having the same wavelength interval is assigned to one channel. Further, in this embodiment,
A channel is individually assigned to each terminal station, and when performing transmission, one of the wavelengths constituting the assigned channel is used as a transmission wavelength. The transmitting optical node can determine which one of the wavelengths constituting the assigned channel is used.

The reception of the data transmitted by the channel having the above-mentioned structure is performed by using A) as a filter of the receiver for selecting the channel to be received (the channel including the wavelength to be received). And B) the wavelength intervals between the peaks are all equal and equal to the wavelength intervals of the wavelengths that make up each channel, and C) it is possible to continuously sweep while maintaining the wavelength intervals. it can. The FFP filter is one of such filters. The FFP filter has a plurality of transmittance peaks of the period FSR, and the wavelength spacing FSR hardly changes before and after the sweep.

In the present embodiment, since reception is carried out by simultaneously using a plurality of transmittance peaks, it is possible to set the transmission wavelength over a wavelength range of ΔλFSR or more as shown in FIG.

FIG. 1 is a diagram showing a method of using wavelengths in this embodiment. The horizontal axis represents the wavelength λ and the vertical axis represents the light intensity. λmin to λmax is the wavelength range used by the system, λ
A to λB are wavelength ranges that can be used as an optical filter.
λf1 to λf5 are center wavelengths (hereinafter referred to as filter transmission wavelengths) of the m to m + 4th-order transmittance peaks of the optical filter at a certain reference moment. In addition, the transmission spectrum of the optical filter at another moment (when the transmission wavelength of the optical filter is matched to the channel to which the wavelength λ3 belongs) is also shown in an overlapping manner.

The solid line represents the optical signal on the transmission line, and the dotted line represents the wavelength not used in each channel. In this figure, λ1, λ2, λ (3,3), λ (4,2) are actually used wavelengths. Λ1 to Λ4 are λ
It is an equivalent wavelength set (described later) to which 1 to λ4 belong.

The above features will be described in more detail.

In the present invention, two arbitrary wavelengths are said to be equivalent when their wavelength difference is an integral multiple of ΔλFSR of the optical filter. The wavelength λ (i, m) equivalent to the wavelength λi can be expressed as λ (i, m) = λi + m · ΔλFSR (m: integer). However, λ (i, 0) = λi.
The transmission peak wavelengths of the FFP filters are equivalent to each other.
For the detector, signals with equivalent wavelengths are equivalent and cannot be distinguished.

A wavelength set Λi of wavelengths equivalent to λi included in the wavelength range λmin to λmax used by the system is called an equivalent wavelength set of λi. That is, Λiε {λ (i, m) | λmin ≦ λ (i, m) ≦ λmax, m: integer}. In other words, the set of wavelengths that can be received simultaneously using the FFP filter is the equivalent wavelength set. For example,
In FIG. 1, the equivalent wavelength set of λ3 is Λ3 = {λ3, λ (3,
1), λ (3,2), λ (3,3)}.

In this embodiment, the one transmission wavelength set is used as one channel. Then, the transmission wavelength of each optical node is determined as follows. 1) In order to prevent interference between wavelengths belonging to different channels, a temporary channel wavelength λi is determined with Δλ being a wavelength interval that does not cause interference. That is, λ1, λ2 = λ1−Δλ, λ3 = λ1-2Δλ. At this time, the provisional channel wavelength is set within one ΔλFSR at the reference moment. The reference moment can be arbitrarily determined. At that time, the sum of the wavelength interval between λ1 and the long wavelength side end of the one ΔλFSR, the shortest wavelength of the provisional channel wavelengths and the short wavelength side end of the one ΔλFSR. Is equal to or greater than Δλ. 2) One set is assigned to each optical node using the equivalent wavelength set Λi of λi as a channel. 3) The optical node to which the equivalent wavelength set Λi is assigned uses its arbitrary element λ (i, k) as its own optical node transmission wavelength.

FIG. 1 shows a state in which four signals are transmitted on the transmission path. Equivalent wavelength set Λ1 as channel
The optical node to which is assigned the wavelength λ1, the optical node to which Λ2 is assigned is λ2, the optical node to which Λ3 is assigned is λ (3,3), and the optical node to which Λ4 is assigned is λ (4, 2)
Are used as transmission wavelengths, respectively.

The relationship between the control voltage VF of the receiving filter on the receiving side and the amplifier output I is as shown in FIG. FIG. 2 is a diagram for explaining the relationship between the filter control voltage and the amplifier output in this embodiment. The horizontal axis is the filter control voltage V
F, the vertical axis represents the amplifier output I. Vf1 to Vf3 are
The filter control voltage when the mth-order filter transmission wavelength matches λf1 to λf3 is shown. V1 to V4 are filter control voltages when the mth-order filter transmission wavelength matches λ1 to λ4. Further, ΔVFSR represents a potential difference corresponding to FSR.

This receiver uses the optical filter m at V1.
Assuming the next transmission wavelength matches λ1, at V2
The transmission wavelength of the m-th order is λ2, the transmission wavelength of the m + third order is λ (3,3) in V3, and the transmission wavelength of the m + second-order is λ in V4.
Matches (4,2). Further, as shown in the figure, on the VF axis, the same signal is repeated every cycle ΔVFSR.
Therefore, the sweep range of the filter control voltage VF required to receive all signals is VFmin to VFmax (= VFmin + Δ
VFSR) is all right. That is, according to the present invention, only by sweeping the filter over one ΔλFSR, one of the plurality of transmission peaks coincides with the desired wavelength, and therefore one Δ
All channels can be detected simply by sweeping over λFSR. In other words, in the present invention, it is recognized as a state in which any one of a plurality of transmission peaks matches one wavelength, without identifying which one of a plurality of transmission peaks matches, and the state in which the one wavelength is It recognizes that the channel to which it belongs is being detected.

Next, the communication procedure of each terminal station in this embodiment will be described. Operation (1) A station in an idle state (a state in which transmission / reception is not performed) sets the control voltage VF of the filter drive circuit to VFmin-
Sweep over VFmax and try to receive. When the operation (2) signal is detected, it is checked whether or not it includes the identification signal addressed to itself. Operation (3) When the identification signal addressed to the own station is included, the control voltage VF of the filter drive circuit is locked. If operation (4) is not included, continue the sweep. Operation (5) If no signal can be detected, stop sweeping the control voltage at VFmax, return to VFmin, and then VFmax again
Start sweep to.

As described above, according to the present embodiment, it is possible to use the entire wavelength range that can be used as a filter as the wavelength range that can be transmitted by the reception control similar to the conventional one. Further, as a result, the LD can be used as a light source even if the wavelength of the LD is wide due to individual differences.

(Embodiment 2) In Embodiment 1, a channel configured with a transmission wavelength is set in advance and each channel is assigned to each optical node. In the present embodiment, the optical node of the terminal station which requests transmission is used. The internal channel is detected, transmission is started at a wavelength that does not cause interference with the channel, and a channel having a wavelength equivalent to the transmission wavelength is occupied until the transmission ends.

The second embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 8 is a block diagram of the optical node 302 of this embodiment. Optical transmitter 801, optical receiver 802, optical splitter 80
Consist of 3. The optical transmitter 801 outputs the transmitted light to the transmission line. The optical branching device 803 branches the signal light from the transmission path and outputs one to the optical receiver 802 and the other to the optical transmitter 801.

FIG. 9 is a block diagram of the optical transmitter of this embodiment. Overall, the wavelength control system 901, LD902, optical filter 90
3, LD drive circuit 904, optical filter drive circuit 905, light receiving element 906, amplifier 907, discriminator 908, optical branching device 909, optical combiner
910, optical switch 911.

The wavelength control circuit 901 is composed of an arithmetic processing circuit, a storage element, an A / D converter, a D / A converter and the like. The LD drive circuit 904 and the optical filter drive circuit 905 are controlled based on a control signal from the terminal station and an output signal from the discriminator 908 to perform a tuning operation. It also stores parameters necessary for operation and operation procedures.

The change amount ΔVLD of the control voltage VLD to the LD drive circuit 904 and the change amount ΔλL of the transmission wavelength λL of the LD902 are
It is assumed to be proportional. Similarly, the optical filter drive circuit
It is assumed that the change amount ΔVF of the control voltage VF to 905 and the change amount ΔλF of the transmission spectrum of the optical filter 903 are proportional. Further, it is assumed that the wavelength control circuit 901 can calculate the LD control voltage ΔVLD similarly corresponding to Δλ from the filter control voltage difference ΔVF corresponding to a certain wavelength difference Δλ.
That is, it can be calculated as ΔVLD = f (ΔVF).

Optical signals from the transmission line and the optical branching device are combined by the optical combiner 910 and are incident on the optical filter 903. The transmitted light is converted into an electric signal by the light receiving element 904 and the amplifier 905. The discriminator 908 outputs H or L of a digital signal depending on the strength of the input signal. The threshold value is preset to the voltage at which the filter reliably detects the optical signal.

The optical branching device 909 branches the output of the LD 902 and outputs one to the optical switch 911 and the other to the optical combiner 910. The optical switch 911 turns ON / OFF the optical circuit based on the control signal of the wavelength control circuit 901, and switches the transmission / non-transmission of the LD output to the transmission path. The optical combiner 910 combines the optical signal from the transmission line and the LD output from the optical branching device 909, and outputs the transmission signals of its own station and other stations to the optical filter 903.

FIG. 10 is a diagram showing a method of using wavelengths in this embodiment. The horizontal axis of the figure is the wavelength λ, and the vertical axis is the signal intensity.
Represents I. In this example, communication is performed at wavelengths λ1 to λ8 which are dispersed and arranged over the wavelength regions of four FSRs. In order to prevent interference, the wavelengths λ1 to λ8 are set so that their equivalent wavelengths do not become less than the channel interval Δλ.

FIG. 11 is a diagram for explaining the relationship between the filter control voltage VF and the amplifier output intensity I in this embodiment. For Vf1 to Vf3, the mth-order filter transmission wavelength is λf1 to
The filter control voltage when it matches λf3 is shown. V
Similarly, 1 to V8 are filter control voltages when the m-th order filter transmission wavelength matches λ1 to λ8. Furthermore, ΔVFSR
Is a filter control voltage corresponding to FSR, and ΔV is a control voltage corresponding to channel spacing Δλ.

FIG. 12 is a diagram for explaining the transmission preparation operation in the communication procedure of each terminal station in this embodiment. 12A to 12C, the horizontal axis represents the filter control voltage V
F, the vertical axis is the discriminator output.

FIG. 12A is a diagram for explaining the operation 1-1 and shows the state immediately before the start of transmission.
Va1 to Vak are the values of the filter control voltage VF when the transmission signal on the transmission line is detected in this operation. VLmi
n to VLmax is the sweep wavelength range λLmin of the LD of an optical node
~ ΛLmax corresponding filter control voltage VF, VFmin ~ VF
max represents the filter control voltage corresponding to the filter sweep range λFmin to λFmax.

In the figure, the sweepable range of the LD is shown as the range VLmin to VLmax of the filter control voltage VF. This corresponds to the range of λLmin to λLmax on the wavelength axis. Similarly, set the filter sweep range to VFmin to VFmax.
Indicated as. This corresponds to the range of λFmin to λFmax for the mth-order transmission peak wavelength. However, if the FSR of the filter is ΔλFSR, then λFmax = λFmin + ΔλF
It is SR. Further, ΔV is the potential difference of the control voltage corresponding to Δλ.

FIG. 12B is a diagram for explaining the operation 1-2, and shows a state in which transmission is started at the wavelength λLmin, but no optical signal is sent out on the transmission line. Vb1 to V
bk + 1 is the value of the filter control voltage VF when the transmission signal on the transmission path is detected in this operation.

FIG. 12C is a diagram for explaining the operations 1-3, and shows a state in which the transmission of the optical signal is started on the transmission line at the wavelength λL '.

FIG. 13 is a diagram for explaining the wavelength shifting operation in the communication procedure of each terminal station in this embodiment. The horizontal axis represents the filter control voltage VF and the vertical axis represents the discriminator output.
VL is a filter control voltage corresponding to the transmission wavelength λL of the own station. The dotted line shows the transmission spectrum of the filter. Further, ΔV is the potential difference of the control voltage corresponding to Δλ. δ
V is a predetermined potential difference, which is a margin for allowing an error or the like with respect to the minimum required sweep potential difference and reliably detecting the transmission wavelengths of the own station and other stations. ΔVj is also a predetermined potential difference and is the amount of movement of the sweep start voltage for moving the sweep range.

FIG. 14 is a diagram for explaining the wavelength interval maintaining operation in the communication procedure of each terminal station in this embodiment. The horizontal axis represents the filter control voltage VF and the vertical axis represents the discriminator output. VL and VL ′ are filter control voltages corresponding to λL and λL ′, respectively. ΔV is the potential difference of the control voltage corresponding to Δλ, and ΔV ′ is the potential difference between VL and VL ′.

FIG. 3 is a block diagram of an optical communication system to which the wavelength control system of this embodiment is applied.

FIG. 6 is a block diagram of the optical receiver in this embodiment.

FIG. 7 shows an optical filter 603 according to this embodiment.
9 is a diagram showing a transmission spectrum of an optical filter 903. FIG.

The description of FIGS. 3, 6, and 7 has been made in the first embodiment, and therefore will be omitted here.

Next, the features of this embodiment will be described.

In this embodiment, both the transmission wavelength of the optical node for transmission and the reception wavelength of the optical node for reception are variable.

As the receiver, the same receiver as in the first embodiment is used. The transmitter includes a variable wavelength light source and a variable wavelength optical filter. This tunable filter is an FFP filter having the same FSR as that used in the receiver.

The transmitter transmits the wavelength of the optical signal on the transmission line by using the FFP filter and grasps the usage status as the positional relationship on the filter control voltage VF axis. That is, the usage status of the channel is detected without discriminating the order of the transmission peak of the transmitted optical signal. Also, V
By keeping the interval (that is, the potential difference) between the channel used by the own node and the adjacent channel on the F axis constant, interference is prevented and the wavelength utilization efficiency is improved.

FIG. 10 shows an example of using the wavelength in this embodiment. In this example, communication is performed at wavelengths λ1 to λ8.

FIG. 11 shows the relationship between the filter control voltage VF of the transmitter and the amplifier output I when the optical filter having the transmission spectrum shown in FIG. 7 is used with the wavelength on the transmission line shown in FIG. . V1 to V8 are wavelengths λ1
Corresponds to ~ λ8.

The transmitter always controls the transmission wavelength λL of its own station and keeps the interval with the other end station on the VF axis constant to prevent interference. For example, it is assumed that the local station is transmitting at wavelength λ5. On the VF axis, V5 corresponds to λ5. The transmitter controls the transmission wavelength λ5 of its own station so that the potential difference V4−V5 between the signal V4 of the other end station and the signal V5 of its own station which are adjacent on the high voltage side on the VF axis matches ΔV.

Next, the communication procedure of each terminal station in this embodiment will be described. The receiving operation is the same as that in the first embodiment, and detailed description thereof will be omitted. The transmission operation will be described below.

Operation 1-1: Transmission Preparation 1 FIG. 12 (a) is a diagram for explaining the operation 1-1.
In operation 1-1, the channel used by another node on the transmission path is grasped before transmission. The wavelength control circuit turns off the optical switch and sets the filter control voltage to VFmi.
Sweep in the range of n to VFmax. The output from the discriminator is monitored at the same time as the sweep, and the filter control voltages Va1 to Vak corresponding to the optical signal on the transmission line (k: the number of terminal stations transmitting)
Is stored.

Operation 1-2: Transmission Preparation 2 FIG. 12 (b) is a diagram for explaining the operation 1-2. In operation 1-2, the relative positional relationship between the transmission wavelength of the own node (the channel to which the wavelength belongs) and the channel being used by another node is grasped. The wavelength control circuit is an optical switch
The LD is oscillated at the transmission wavelength λL = λLmin in the OFF state. Next, the filter control voltage VF is swept in the range of VFmin to VFmax. At the same time, the output from the discriminator is monitored, and the filter control voltages Vb1 to Vbk + 1 corresponding to the optical signal on the transmission line and the own node transmission signal are stored.

Va1 to Vak obtained in operation 1-1 and Vb1 to Vbk + 1 obtained in operation 1-2 are compared to obtain the filter control voltage VL corresponding to the transmission wavelength λLmin of the own station. In the figure, VL = Vb3. Then Va1 to Vak, and VFma
Focusing on the potential difference ΔVal (= Val + 1-Val) for x,
Find a potential difference ΔVam (= Vam + 1−Vam) corresponding to A) 2ΔV or more and B) the shortest wavelength side. It means that if a potential difference of 2ΔV or more cannot be found, a channel that can be used for transmission cannot be provided.
-1 and repeat operations 1-1 and 1-2, 2ΔV
It waits until the above potential difference occurs, that is, transmission is possible and a channel can be created.

Operation 1-3: Start of Transmission FIG. 12C is a diagram for explaining the operation 1-3. In operation 1-3, the own station transmission wavelength is determined and transmission is started. The wavelength control circuit sets the filter control voltage VF to VF = Vam + ΔV based on Vam found in operation 1-2. Then, the control voltage to the LD drive circuit is swept and fixed when the output of the discriminator becomes H. As a result, the emission wavelength of the LD coincides with the transmission wavelength of the filter set to a wavelength that does not interfere with other channels.
Turn on the optical switch to start transmission. After that, the channel consisting of the wavelength emitted by this LD and its equivalent wavelength is used by this optical node. However, since the wavelength of light emitted by the LD changes as shown below, the equivalent wavelengths constituting this channel also change accordingly.

Operation 2: Wavelength shift FIG. 13 is a diagram for explaining the operation 2. In operation 2, while transmitting, the transmission wavelength λL is changed to the long wavelength side. The wavelength control circuit sets the filter control voltage VF to VF = VL−δ based on the filter control voltage VL corresponding to λL.
Set to V. Then, VF is swept up to VL + ΔV + δV. At this time, VF when detecting the own station transmission wavelength λL is VL
Memorize as. Further, when the other station transmission wavelength λL 'is detected, VF at that time is stored as VL'. here,
δV is a predetermined potential difference ΔV >>δV> 0, which is a margin for surely detecting the transmission wavelengths of the own station and other stations.

When the transmission wavelength λL 'of another station is detected during the sweep, it is within the sweep range in this operation, that is, ΔV is 2δ.
Since there are a channel used by the own node and an adjacent channel in the range where V is added,
Move to operation 3. If it cannot be detected, it means that the channel used by the own node and the adjacent channel are sufficiently separated.Therefore, in order to bring the interval close to the predetermined interval, the transmission wavelength λL of the own station is set to a predetermined value. The value Δλj is moved to the adjacent channel side. Specifically, the LD control voltage ΔVLDj corresponding to Δλj is added to the LD control voltage up to that point.
Also, the filter control voltage is moved by the sweep start voltage by ΔVj which is the filter control voltage corresponding to Δλj (that is, VF = VL−δV + ΔVj), and the operation 2 is repeated. Each time this operation is repeated, the sweep range and the emission wavelength of the LD of its own node move to the adjacent channel side, that is, the long wavelength side here. Here, Δλj is a predetermined wavelength such that Δλ>Δλj> 0. Therefore, ΔVj is a predetermined potential difference such that ΔV>ΔVj> 0. This value of Δλj is the minimum wavelength interval that allows the filter to follow the change in wavelength and also secures the crosstalk necessary for the system in order to prevent interference.
Then, it is set such that Δλ−Δλj ≧ Δλct.

Further, the transmission wavelength λL of the local station is the longest wavelength λLmax
If it reaches, the transmission wavelength shift is stopped and λL = λ
Continue sending with Lmax.

Operation 3: Maintenance of Wavelength Interval FIG. 14 is a diagram for explaining the operation 3. The horizontal axis is V
F, the vertical axis is the discriminator output. Let the filter control voltages VF corresponding to λL and λL ′ be VL and VL ′, respectively. Also, λ
The LD control voltage corresponding to L is VLD, and the terminal transmitting λL ′ is terminal s. In operation 3, while transmitting, V
The potential difference ΔV ′ (= VL′−VL) from the adjacent terminal station on the F axis is always matched with ΔV.

The wavelength control circuit sets the filter control voltage VF to VF = VL-δV. Next, let VF be VF = VL + ΔV
Sweep to + δV, detect λL and λL ', and obtain VL and VL'. In addition, the difference between the potential difference ΔV ′ and ΔV ΔVerr (ΔVerr =
ΔV−ΔV ′) is obtained. Further, the LD control voltage ΔVLD_err corresponding to ΔVerr is calculated as ΔVLD_err = f (ΔVer
r) Finally, the new LD control voltage VLD_ne
Let w be VLD_new = VLD + ΔVLD_err, and change the transmission wavelength of the own station. As a result, the potential difference between the adjacent terminal station on the VF axis is maintained at ΔV.

After the above operation, the operation 3 is repeated again.

When this operation 3 is repeated and the channel spacing is maintained at a predetermined spacing, if the wavelengths of the adjacent channels change greatly or disappear, V
Even if F is swept up to VL + ΔV + δV, the transmission wavelength of other stations cannot be detected, so in that case, move to operation 2 and set the channel interval between the greatly changed adjacent channel or a new adjacent channel to a predetermined interval. Control to maintain

In the present embodiment, with respect to the transmission wavelength of each terminal station, transmission is started from the short wavelength side and then changed to the long wavelength side. However, a method may be used in which transmission is started from the long wavelength side and then changed to the short wavelength side.

As described above, according to this embodiment, it is possible to use the entire wavelength range that can be used as a filter. As a result, the LD can be used as a light source even if the wavelength of the LD covers a wide range due to individual differences. Further, since it is not necessary to allocate channels in advance, the channels can be effectively used. In addition, since the intervals between the channels are maintained at a predetermined interval, it is possible to effectively use the area where the channels can be formed. In addition, a predetermined channel interval can be maintained at all times regardless of changes in the external environment, and absolute wavelength control such as temperature control is not necessary.

(Other Embodiments) The components are not limited to those described in the embodiments as long as they have similar functions.

In the present invention, particularly in the second embodiment in which the transmission wavelength is tuned, it is desirable to use a light emitting device capable of high-speed tuning. In the above embodiment, L
As D, a 3-electrode λ / 4 shift LD was used. However, any light source capable of continuously changing the oscillation wavelength can be used as the light source of the present invention. For example, the publication Electronics Letters, 1987, Volume 23, 7
Issue, Pages 325-327, "1.55 μm WAVELENGTH TUNABLE FBH-DBR L
Multi-electrode DBR (Distributed Bragg Reflec) described in "ASER"
tor) -LD can be used. Fast tuning of this device is possible.

In the above embodiment, the FFP filter is used as the optical filter having a simple structure and capable of sweeping the transmission wavelength over a wide range. However, any optical filter having a periodic transmittance peak and capable of continuously changing the wavelength of the transmittance peak can be used. For example, the Journal Journal of lightwave
technology, 1989, Volume 7, Issue 4, pages 615-624, “Angle-Tuned Et
alon Filters for Optical Channel Selection in High
Density Wavelength Division Multiplexed Systems ”
It is possible to use the described FP etalons. Also, Journal of lightwave technology, 1993, 11
Volume, No. 12, 2033-2043, "Tunable Liquid-Crystal Fabry-
Perot Interferometer Filter for Wavelength-Divisio
Liquid crystal F described in "n Multiplexing Communication Systems"
A P filter may be used.

Furthermore, it is also possible to use a dielectric multilayer filter as the optical filter. In this case, the n wavelengths of the transmission wavelengths λi (i = 1, 2, ..., N) are made to be equal to the FSR.

In the above embodiment, the wavelength spacing of the two wavelengths closest to each other (equivalent wavelength spacing) of the equivalent wavelengths belonging to one channel is the wavelength spacing FSR of the transmittance peak of the optical filter of the receiver. Equal to. However, in the present invention, the wavelength interval of the transmittance peak of the optical filter of the receiver may be a natural multiple of the wavelength interval of the equivalent wavelength. However, in order to receive all channels, the optical filter of the receiver must include at least the wavelength range used by the system within its usable wavelength range. In addition, it is necessary to be able to sweep the transmittance peak for at least the smaller wavelength interval of the transmittance peaks of the optical filter of the receiver or the wavelength range used by the system.

Although an optical fiber is used as the optical transmission line in the above-mentioned embodiment, the present invention is not limited to this.
A place where an optical signal can exist, such as an optical path using an optical system or a space, can be used as an optical transmission path.

[0095]

As described above, according to the invention of the present application, the sweep range of the optical filter at the time of receiving is expanded without expanding the interval of the transmittance peak of the optical filter at the time of receiving. The wavelength range used in the system can be expanded without doing so. Further, it is possible to allow variations in the oscillation wavelength of the light source, eliminate the need for wavelength selection, and increase the yield.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method of using wavelengths according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a relationship between a filter control voltage and an amplifier output in the first embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical communication system to which the wavelength control system according to the first embodiment of the present invention is applied.

FIG. 4 is a configuration diagram of an optical node according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical transmitter according to the first embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical receiver according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a transmission spectrum of the optical filter according to the first embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical node according to a second embodiment of the present invention.

FIG. 9 is a configuration diagram of an optical transmitter according to a second embodiment of the present invention.

FIG. 10 is a diagram showing a method of using wavelengths according to the second embodiment of the present invention.

FIG. 11 is a diagram for explaining the relationship between the filter control voltage VF and the amplifier output intensity I in the second embodiment of the present invention.

FIG. 12 is a diagram for explaining a transmission preparation operation in the communication procedure of each terminal station in the second embodiment of the present invention.

FIG. 13 is a diagram for explaining the wavelength shift operation in the communication procedure of each terminal station in the second embodiment of the present invention.

FIG. 14 is a diagram for explaining a wavelength shift operation in the communication procedure of each terminal station in the second embodiment of the present invention.

FIG. 15 is a diagram showing a method of using wavelengths in a conventional example.

[Explanation of symbols]

 301-1 to 301-n Terminal station 302 to 302-n Optical node 303 to 303-n nxn Star coupler 304 to 304-n Transmission optical fiber 305 to 305-n Reception optical fiber 401 Optical transmitter 402 Optical Receiver 501 Wavelength control circuit 502 LD drive circuit 503 LD 504 Light receiving element 505 Amplifier 506 Temperature controller 507 Optical branching device 601 Wavelength control circuit 602 Optical filter driving circuit 603 Optical filter 604 Light receiving element 605 Amplifier 801 Optical transmitter 802 Optical receiver 803 Optical branching device 901 Wavelength control circuit 902 LD 903 Optical filter 904 LD driving circuit 905 Optical filter driving circuit 906 Light receiving element 907 Amplifier 908 Discriminator 909 Optical branching device 910 Optical junction device 911 Optical switch

Claims (13)

[Claims] 1. An optical communication method in an optical communication system in which a plurality of optical nodes are connected by an optical transmission line, and a plurality of channels are multiplexed in the optical transmission line to perform communication, wherein each of the plurality of channels is provided. A predetermined first to each other
An optical node that is configured by a wavelength group including a plurality of wavelengths having a wavelength interval of, and that transmits is one wavelength in the wavelength group that configures one channel, and an optical node that receives is A light detecting means for detecting light in an optical transmission path, wherein the light detecting means has a plurality of detection rate peaks which are natural multiples of the predetermined first wavelength interval, An optical communication method, characterized in that reception is performed by matching wavelengths forming a group. 2. A second wavelength which does not interfere with each other at least wavelengths which are closest to each other and belong to different channels so that wavelengths belonging to different channels do not cause interference.
The optical communication method according to claim 1, wherein the optical communication methods are arranged at the wavelength intervals. 3. A plurality of wavelengths are arranged at the second wavelength interval so as to be within the predetermined first wavelength interval, and the plurality of wavelengths belong to different channels from each other. 2. The optical communication method described in 2. 4. The optical communication method according to claim 1, wherein the plurality of channels are assigned to each optical node that performs the transmission. 5. The optical node that performs the transmission is a photodetector that detects light in the optical transmission line, and has a plurality of detection rate peaks at the predetermined first wavelength interval. A channel being used is detected by sweeping at least the predetermined first wavelength interval, and transmission is performed at one wavelength of a wavelength group forming a channel that does not cause interference with the channel being used. 1. The optical communication method described in 1. 6. The optical node performing the transmission detects channels in use in the optical transmission path, including channels transmitted by the own node, by the light detecting means, and thereby the channel transmitted by the own node. And a channel between another channel being used and a channel detected closest to the channel transmitted by the self node, and controlling the wavelength transmitted by the self node to maintain the gap at a predetermined interval. 5. The optical communication method described in 5. 7. An optical communication system in which a plurality of optical nodes are connected by an optical transmission line, and a plurality of channels are multiplexed in the optical transmission line to perform communication, wherein each of the plurality of channels is mutually predetermined. First of
The optical node that performs transmission has a transmission means that performs transmission at one wavelength in the wavelength group that constitutes one channel. The receiving optical node is a photodetecting unit that detects light in the optical transmission line, and has a plurality of detection rate peaks that are natural numbers times the predetermined first wavelength interval, An optical communication system comprising: a means for matching a light detection rate peak of the light detecting means with a wavelength forming a wavelength group of a desired channel. 8. A second wavelength converter which does not interfere with at least wavelengths which are closest to each other and belong to different channels so that wavelengths belonging to different channels do not cause interference.
The optical communication system according to claim 7, wherein the optical communication systems are arranged at the wavelength intervals. 9. The plurality of wavelengths are arranged at the second wavelength interval so as to be within the predetermined first wavelength interval, and the plurality of wavelengths belong to different channels from each other. 8. The optical communication system according to item 8. 10. The optical communication system according to claim 7, wherein the plurality of channels are assigned to each optical node that performs the transmission. 11. The optical node that performs the transmission is a photodetector that detects light in the optical transmission line, and has a plurality of detection rate peaks at the predetermined first wavelength interval. , The light detection rate peak of the light detecting means is set to the predetermined first
8. The optical communication system according to claim 7, further comprising: a means for changing the wavelength interval while maintaining the wavelength interval, and having a function of sweeping the light detecting means to detect a channel in use. 12. The optical node performing the transmission includes a control means for controlling a wavelength transmitted by the own node, and a channel in use in the optical transmission path including a channel transmitted by the own node by the light detecting means. Detecting the interval between the channel transmitted by the node and the channel detected closest to the channel transmitted by the node among other used channels, the node transmits the interval. 12. The optical communication system according to claim 11, further comprising means for controlling a wavelength to be maintained to maintain a predetermined interval. 13. The optical communication according to claim 7, wherein the light detecting means has a periodic transmittance peak, and includes an optical filter capable of controlling the transmittance peak while maintaining the period. system.